THE  THEORY  OF  COPPER  DEPOSITION. 

By  Alfred  C.  Lane,  State  Geologist,  Lansing,  Micli.* 

During  the  past  few  years  there  has  been  a lively  interest 
in  the  theory  of  the  origin  of  ore  deposits*  and  recently  two 
works  have  been  published  by  the  Institute  of  Mining  EngA 
neers  and  by  the  Engineering  and  Mining  Journal , which  give 
a very  good  account  of  the  present  state  of  the  controversy, 
and  references  enough  to  carry  one  pretty  well  over  the  whole 
field  of  the  latter.f  In  these  discussions  our  deposits  of  iron 
ore  and  coppe'r  of  lake  Superior  have  been  frequently  used  as 
illustrations  of  the  various  theories-  by  those  who  take  part 
in  the  discussion.  In  view  of  these  facts,  it  seems  proper  to 
give  a review  of  what  is  known  concerning  the  copper  of  lake 
Superior  and  of  the  theories  regarding  the  same.  There  is  also 
a practical  interest  involved  in  the  discussion.  As  we  shall 
shortly  see,  all  fhe  best  authorities  at  present  agree  that  the 
copper  has  been  deposited  by  water,  but  there  is  some  differ- 
ence of  opinion  as  to  whether  the  water  current  is  a de- 
oyscending  one  and  copper  was  deposited  and  a circulation  pro- 
duced by  gravity,  or  ascending,  and  the  circulation  due  to 
£-  one  or  more  principal  causes,  which  we  may  call  as  a common 
^ name,  volcanic,  meaning  thereby  that  they  are  connected  with 
the  interior  heat  of  the  earth.  Now,  it  is  a common  notion 
• y among  the  practical  Cornish  miners  of  the  copper  country,  al- 
though I do  not  remember  to  have  seen  the  statement  in 

* print,  that  the  copper  is  liable  to  occur  under  high  ground. 

To-  understand  what  is  meant  by  the  expression  “high 

* _ ground,”  we  must  remember  that  at  the  present  day  the  bulk 

of  the  copper  is  deposited  in  bedded  lodes.  It  would  be  per- 
haps more  correct  to  say  that  it  comes  from  lodes  whose  strike 


* Advance  sheets  from  the  Annual  Report  for  1903,  reprinted  from  The 
Michigan  M iner,  January  and  February,  1 904.  It  should  be  understood  that 
the  title  in  a general  magazine  like  the  American  Geologist  is  too  broad,  lor 
the  article  has  reference  solely  to  the  deposits  of  Keweenaw  Point,  and  the 
author  does  not  wish  to  apply  either  facts  or  conclusions  to  other  deposits, 
such  as  the  sulphides,  whose  history  he  believes  to  be  different. 

f Genesis  of  ore  deposits.  Reprinted  papers  from  Volumes  xxiij,  xxiv,  xxx 
and  xxxi  of  the  Transactions  of  the  Ameiican  Institule  of  Mining  Engineers. 
Published  by  the  Institute  at  the  office  of  the  Secretary,  New  York-City.  1902. 

Ore  Deposits,  a discussion  republished  from  the  Engineering,  and  Mining 
Journal,  New  York  City,  1903. 

See  also  Geological  Survey  of  Michigan,  vol.  i,  Part  II,  p.  43.  Vol.  vi, 
Part  I,  p.  216. 

Yet  more  recent : Trans.  Am.  Inst  Min.  Eng. , Oct. , 1 902.  “Igneous  Rocks 
and  Circulating  \v  aters  as  Factors  in  Ore  Deposition,’’  by  J.  F.  Kfmp;  “Ore 
Deposits  Near  Igneous  Contacts,’’  by  W.  H.  Weed,  and  discussion  of  same. 
Annual  report  of  the  State  Geologist  (of  New  Jersey ),  1902.  “Copper  De 
posits  of  New  Jersey,”  by  Walter  Harvey  Weed.  “The  Chemistry  of  Ore 
Deposition,”  by  Walter  P.Jenney. 


P 1426 1 


298 


The  American  Geologist. 


November,  1904. 


is  the  same  as  that  of  the  beds  of  the  Keweenaw  formation. 
It  is  commonly  accumulated  in  the  originally  more  porous  parts 
of  the  beds.  Sometimes  these  porous  parts  are  sandstones 
and  conglomerates,  but  more  often  they  are  porous  upper 
parts  of  lava  flows.  It  is,  I believe,  true  that  in  many  cases 
there  are  faults  parallel  to  the  bedding  planes,  or  - so  nearly 
so  that  the  difference  has  not  been  detected,  which  have  had  an 
important  influence  on  the  production  of  copper.  In  some  cases 
we  know  there  are  such  faults,  which  generally  have  a some- 
what steeper  dip  than  that  of  dips  generally.* 

Nevertheless,  in  a practical  way  the  most  characteristic 
feature  of  these  lodes  is  the  porous  beds.  Any  one  of  these 
porous  beds  may  contain  copper  and  there  are  few  of  them, 
which  are  decomposed,  that  do  not  show  some  trace  of  copper. 
But  the  parts  which  are  relatively  rich,  rich  enough  to  be 
the  sole  object  of  interest  to  the  miner,  are  rare,  and  the  mean- 
ing of  the  idea  that  copper  occurs  along  high  ground  is,  as 
I understand  it,  that  in  following  the  outcrop  of  such  lode, 
chutes  of  copper  are  liable  to  occur  where  the  outcrop  of  the 
lode  is  extra  high.  Now  there  is  some  ground  for  this  idea. 
If  we  take  the  Baltic  lode,  just  developed,  we  find  that  in  the 
Baltic,  Trimountain  and  Champion  mines  this  is  rich,  while 
just  northeast,  on  seqtion  i6f  the  Atlantic  mine  has  done  a 
good  deal  of  exploring  without  being  able  to  find  the  lode. 
Rising  once  more  on  the  high  land  we  find  the  Isle  Royale 
mine  close  to  the  deep  trough  of  Portage  lake,  where,  on  the 
other  side,  is  the  Quincy  mine,  on  high  land  again.  The 
Sheldon  and  Columbia  and  Hancock  mines,  more  down  in  the 
Portage  Lake  valley,  do  not  appear  to  have  been  so  successful. 
Going  farther  north,  we  find  the  Calumet  & Hecla,  Tamarack, 
Kearsarge  and  Wolverine  mines,  not  very  far  from  the  Allouez 
gap  on  the  southwestern  side ; on  the  northeastern  side  is  the 
Mohawk  mine.  -Nearer  the  gap  is  the  Ahmeek  property,  which 

* The  top  of  the  Calumet  and  Hecla  is  markedly  slickensided.  See  also 
Volume  vi  Part  II,  pp.  86-94;  the  slide  fault  in  the  Central  mine  appears  to  be 
nearly  parallel  to  the  Kearsarge  conglomerate.  The  accumulation  of  copper 
was  in  the  pin  above  this  slide,  and  on  reaching  the  conglomerate  they  work- 
ed on  top  of'it  finding  good  copper  ground. 

The  annual  report  of  the  Phoenix  mine  for  1901  shows  in  the  section  by 
Dunb*k  D.  Scott,  the  steeper  fault  slide  in  that  mine,  in  the  St  Clair  vein. 
The  old  Minnesota,  now  Michigan  mine,  had  its  largest  deposit  of  copper 
where  a steeper  fissure  intersected  a lode.  See  the  report  of  the  C ommissioner 
of  Mineral  Statistics  for  1880.  p.  76.  Copper  Handbook,  1902.  p.  195. 

f Volume  vi,  Part  II,  Plate  10. 


The  Theory  of  Copper  Deposition— Lane,  299 

is  just  being  opened  up  and  whose  true  valu£  has  not  been 
determined.  If  the  “high  ground”  notion  has  any 
substantial  basis,  its  prospects  would  not  be  so  good  as  those 
of  the  Mohawk  and  Wolverine  mines,  although  it  lies  on  the 
same  lode  and  between  them.  The  Phoenix  mine  and  the 
Cliff  lie  011  higher  land,  not  far  from  the  gap  of  Eagle  river, 
and  turning  to  the  other  end  of  the  range  we  find  the  Minne- 
sota and  the  National  on  one  side  and  the  Victoria  on  the 
other  of  the  gap  made  by  the  Ontonagon  river,  while  the  Mass 
and  Adventure  lie  on  the  high  land  between  the  Flint  and  the 
Fire  Steel  rivers. 

Now,  this  grouping  of  mines  in  accordance  with  this  notion 
that  the  copper  occurs  on  the  high  ground  may  be  due  to  the 
fact  that  the  porous  beds  are  usually  eroded,  and  therefore 
not  exposed,  and  not  easily  exploited  or  developed,  except  on 
high  ground.  It  might  also'  be  suggested  that  the  alterations 
which  produce  the  copper  had  cemented  these  beds  more  firm- 
ly and  had  thus  given  a greater  resistance  to  erosion,  either 
by  ice  or  by  water.  The  copper  itself,  however,  even  in  the 
richest  mines,  is  only  a small  fraction  of  the  rock,  and  is 
easily  decomposed  chemically,  and  so  are  some  of  the  asso- 
ciated minerals,  and,  although  at  times,  copper  bearing  amyg- 
daloids,  as  the  igneous  porous  beds  are  called,  are  more  or  less 
saturated  with  silica  and  epidote,  I do  not  think  those  minerals 
are  so  characteristic  of  the  copper-bearing  lodes  as  to  lead 
to  a relatively  greater  elevation  of  such  parts  of  the  lode. 
However,  there  is  room  here  for  inquiry. 

I leave  tp  the  last  another  possible  explanation  which  has 
a more  direct  connection  with  the  theory  of  the  deposits  of 
the  copper.  If  the  copper  is  deposited  by  descending  waters, 
as  Piumpelly,  who  has  done  by  far  the  most  work  upon  the 
subject,  suggested,  and  the  motion  of  these  descending  waters 
is  determined  by  gravity,  descending  along  the  lodes  at  one 
branch  of  the  inverted  siphon  and  rising  either  in  the  same  lode 
at  a lower  point  of  its  outcrop,  or  in  some  cross  fissure,  which 
might  very  well  be  the  cause  of  the  gap  in  the  range,  then  we 
can  readily  see  that  the.  greatest  activity  and  circulation  and 
greatest  deposition  of  the  copper  consequently,  should  be 
beneath  salient  points  of  the  outcrop  of  the  lode.  Take  for 
instance,  the  Calumet  & Hecla.  That  deposit  outcrops  600  or 


300  The  American  Geologist.  November,  1904. 

700  feet  above*  Lake  Superior,  and  the  chute  of  the  richer 
streaks  in  the  deposit  is  northward,  and  we  may  imagine  the 
waters  working  down  in  that  direction  to  re-appear  over  in 
the  Allouez  gap  or  up  some  fissure  which  may  possibly  have 
' determined  the  gap.  We  see,  therefore,  that  the  question  as  to 
whether  the  copper  was  deposited  by  waters  circulating  in 
one  fashion  or  another  has  a practical  interest  in  guiding  the 
search  for  the  richest  parts  of  the  lode.  Moreover,  Van  Hise 
has  suggested  that  the  richer  parts  of  the  lode — called  chutes — 
will  be  found  beneath  upward  bends  if  the  waters  of  deposi- 
tion are  ascending,  beneath  downward  bends  if  the  waters  of 
deposition  are  descending.  If  he  is  right,  which  I doubt,  in  say- 
ing that  the  copper  of  the  Michigan  lodes  are  deposited  by 
ascending  waters,  the  southern  end  of  the  Ahmeek  and  the 
northern  part  of  the  Kearsarge  properties  should  be  extra  pro- 
ductive according  to  Hubbard’s  map  of  the  Allouez  gap  area 
(Volume  VI.,  Part  II.,  Plate  VII.),  but  if  the  waters  are  de- 
scending, the  same  area  should  be  lean. 

In  the  first  place  we  may  premise  that  it  is  a settled  ques- 
tion that  the  copper  was  deposited  by  water.  All  kinds  of 
authority  agree  in  this,  although  at  one  time  a few  geologists 
thought  of  its  being  inserted  in  a molten  state.  But  native 
copper  and  native  silver  occur  together,  as  they  could  not  if 
they  were  melted.  They  would  at  once  be  alloyed.  Jewelry  is 
often  made  of  sections  of  nuggets  of  copper  and  silver,  popu- 
larly known  as  halfbreeds,  where  the  sharp  and  irregular  line 
between  the  copper  and  silver  is  beautifully  displayed.  We  also 
find  copper  grown  upon  minerals,  like  analcite  and  prehnite, 
which  one  can  fuse  in  a candle  flame.  It  is  not  very  rare  to 
find  a sharp  crystal  of  dog-tooth  spar  entirely  plated  over 
with  copper,  and  then  the  growth  taken  up  again.*  Pumpelly 
has  given  in  Volupie  I.  of  our  reports  a most  thorough  dis- 
cussion of  the  way  in  which  the  copper  occurs.  A very  in- 
teresting specimen,  owned  by  Dr.  Hubbard,  shows  a crystal  of 
quartz  which  has  been  corroded  and  mainly  by  native  cop- 
per. Moreover,  in  the  deeper  part  of  the  Quincey  mines,  Dr. 
Koenig  has  found  a water  which  is  now  depositing  copper  and 
contains  9 grams  to  the  metric  ton  of  the  same. 

* See  Volume  i,  Part  II,  Chapter  III;  also  Volume  vi,  Part  II,  pp.  163  to 
165  of  our  reports. 


The  Theory  of  Copper  Deposition — Lane.  301 

I have  shown  in  my  United  States  Geological  Survey  water 
supply  paper  No.  31,  on  the  different  waters  of  Lower  Michi- 
gan, that  while  each  porous  bed  varies  in  its!  character  of 
water  from  point  to  point,  yet  there  is  little  inter  communication 
between  them  and  it  is  difficult  to  see  how  there  could  be  much, 
except  upward  along  fissures  or  drill  holes.  Beds  of  clay  or 
shale  are  known  to  be  so  impervious  to  water  and  to  oil,  they 
may  be  taken  to  be,  even  in  a geological  sense,  impervious 
layers,  permanently  guiding  and  separating  the  different  flows 
of  water.  The  same  statement  applies  to  clayey  belts  of  de- 
composed rock,  paint  rock  and  fluccan,  as  Van  Hise  himself  has 
ably  pointed  out  in  discussing  chutes  and  the  formation  of  the 
Galena  lead  deposits.  Thus,  it  must  be  remembered,  that  Van 
Hise’s  figures  of  underground  flow  apply  only  to  a homo- 
geneous medium.  His  figure  5,  for  instance,  might  represent 
the  flow  of  water  in  one  single  porous  bed,  say  of  conglomerate, 
■sandstone,  or  amygdaloid,  but  not  the  formation  at  random. 
It  is  by  no  means  practically  true,  therefore,  that  the  zone  of 
fracture  “will  be  searched  to  its  base  by  moving  waters,”  un- 
less first  it  is  not  only  potentially  but  really  fractured,  so  as  to 
make  it  practically  porous  as  a whole,  and  unless,  also,*  it  is 
covered  by  a surface  topography  so  rough  as  to  stimulate 
circulation.  These  two  conditions  will  be  best  fulfilled  in  those 
mountainous  districts,  which  as  Van  Hise  remarks,  are  most 
liable  to  contain  ore  deposits,  page  416. 

Now,  the  difficulty  in  supposing  that  the  copper  deposits 
are  due  to  such  a general  circulation  of  water  taken  in  at  the 
surface,  as  Van  Hise  imagines  are  very  great.  The  following 
is  a sample  of  water  from  the  Arcadian  shaft,  a relatively  shal- 
low shaft,  analyzed  by  Dr.  Koenig,  August  23,  1898: 


CaCOs 32.7 

j Fe2  03 13.7 

( Kaolin 100.0 

FeC03 24.5 

Mg  C03 25.6 

K2  C03 10.9 

Na2  S1O3 101.3 

Na  Cl tr. 

Na3  P2  05 2.2 

Ne2  C03 42.3 

Organic  matter 82.0 


Total 435.2 


302  The  American  Geologist.  November,  1904. 

While  a deep  mine  water  coming  in  at  the  46th  level  of  the 
Quincy,  analyzed  by  Dr.  Koenig,  was  as  follows : 

Sp.  Gr 1.1898 

Ca  CJ2 17.91 

Na  Cl 2.96 

Mg  Cla 

S03 0 

Iron 0.004 

Copper 0.009 

C02 0.00 

/ 

Now  these  two  analyses  are  typical. 

The  deep  waters  are  strong  solutions  of  earthy  chlorides. 
A water  with  nearly  1 per  cent,  of- bromine  oozes  in  the  45th 
level  of  the  Tamarack.  The  shallow  waters  are  high  in  alka- 
lies, and  so  low  in  chlorine  that  the  alkalies  have  to  be  com- 
bined with  other  acids.  It  is  no  wonder  that  alkaline  zeolites 
occur  in  the  upper  levels.  One  might  explain  the  loss  of  car- 
bonates if  the  upper  water  was  descending  by  a precipitation 
of  the  same  such  as  we  know  has  taken  place,  but  I do  not  see 
that  wq  can  so  explain  the  presence  and  absence  of  chlorine. 
That  must,  it  seems  to  me,  have  been  an  original  constituent 
of  the  deeper  rock  moisture,  either  of  the  sea  in  which  the 
rocks  were  laid  down,  or  of  the  igneous  magna.  Prof.  Moore 
in  his  presidential  address  before  the  Liverpool  Geological  So- 
ciety (1903,  p.  269)  has  shown  that  at  the  top  of  a 96  foot 
thick  intrusive  sheet  there  is  a 10  to  15  foot  belt,  corresponding 
to  the  amygdaloids  of  the  Keweenawan  series,  which  contains 
a little  over  4 per  cent,  carbonic  oxide  and  2.6  per  cent,  water 
which  are,  as  he  believes,  probably  primary.  Analysis  of  the 
Lighthouse  Point  dyke,  which  is  probably  one  of  the  Keweenaw 
flow  feeders,  shows  chlorine,  more  than  enough  to  go-  with  P2 
05  for  apatite,  and  the  apatite  which  has  been  so  commonly 
observed  (Vol.  VI,  Part  1)  also  contains  chlorine. 

Note  the  apparent  concentration  of  the  early  formed  oli- 
vine at  the  margin. 

Moreover  around  volcanic  centers  the  escape  of  vapors 
containing  chlorine  and  carbonic  oxide  and  the  formation  of 
crusts  of  iron  chloride  are  common. 

Pumpelly  furthermore  concludes  that  the  water  which  de- 
posited the  copper  was  descending.  One  of  the  arguments 
which  he  used  is  that  the  alkaline  silicates  abound  in  the  upper 


The  Theory  of  Copper  Deposition — Lane. 


303 


ANALYSES  OF  STONE  FROM  LIGHTHOUSE  POINT  MARQUETTE. 


June  30, 

1903. 

Si02 

46  98 

47.67 

57.25 

47.10 

ai2  o3 , 

17.85 

17.55 

18.10 

17.47 

Fe2  O3 

3.13 

2.51 

2.21 

2.66 

FeO 

10.30 

12.69 

12.42 

12.93 

MoO 

7.10 

5.65 

6.35 

6.88 

CaO 

S 47 

10.75 

11.45 

10.27 

Sodium  Oxide 

2.04 

2.21 

1.9S 

1.91 

-Potassium  Oxidt' 

.60 

.65 

.66 

.59 

H2  0 at  about  800°  C... 

1 97 

.35 

Ho  Oat  110°  C :... 

1.55 

*40 

C02 

.20 

.18 

P2  05 

143 

.169 

.158 

.161 

S 

097 

.183 

.086 

.111 

Cl 

07 

‘ .05 

.02 

.09 

M11O 

26 

.19 

.18 

.15 

101.880 

102.422 

100.744 

109.522 

Center 

Distance  from  margin.... 

Margin 

616m 

4115m 

7600m 

E.  E. 

Ware  under 

direction 

of  E.  D.  Campbell. 

levels  and  are  (page  40)  rare  in  depth;  “in  other  words  they 
are  abundant  in  that  zone  of  the  veins  which  lies  between 
walls  of  those  portions  of  the  beds  of  the  melaphyre  in 
which  we  should  look  for  the  most  advanced  stages  of  altera- 
tion in  the  components  of  melaphyre  supposing  such  alteration 
to  be  due  to  the  action  of  descending  solution.”  By  alkaline 
silicates  he  means  analcite,  apophyllite,  orthoclase  (and  datolite 
is  of  the  same  age).  Copper  occurs  of  similar  age  in  some  of 
these  deposits.  In  studying  the  alteration  of  the  lava  flows 
which  form  so  large  a proportion  of  the  Kewuenawan  series, 
I find  that  the  olivine  is  first  to  alter,  then  the  augite,  and 
lastly  the  feldspar. 

There  are  other  arguments  which  may  be  used  to  support 
Pumpelly’s  theory  with  regard  to  the  origin  of  copper.  As 
has  been  said,  down  to  say  500  or  600  feet  the  water  of  the 
mine  is  quite  fresh.  In  the  deeper  mines  while  there  is  very 
little  water  it  is  an  extremely  strong  solution  of  chlorides.  The 
line  between  the  two  classes  of  water  is  reported  to  be  very 
sharp,  and  there  is  a chance  for  a very  interesting  investiga-, 
tion  right  here.  It  would  seem  quite  difficult  to  suppose  a 
circulation  of  this  heavy  water  up  into  a light  fresh  water, 
especially  under  high  ground,  and  to  imagine  that  there  could 


304 


The  American  Geologist. 


November,  1904. 


be  a sharp  line  between  them.  One  would  expect  to  find  brack- 
ish waters  clear  to  the  surface,  and  that . even  if  the  heavy 
waters  rising  were  diluted  by  affluents,  they  would  retain  the 
same  general  character,  whereas  the  surface  waters  and  the 
deep  waters  are  chemically  entirely  different.  If  there  was  a 
tendency  for  the  waters  to  descend,  however,  the  rocks 
might  naturally  draw  in  fresh  water  of  entirely  different 
'character  from  the  outcrop. 


Figure  illustrating  original  cavities  in  a rock  of  the  copper  bearing  series 
such  as  may  have  been  originally  filled  with  chlorine  gases,  as  at  “A”  wedged 
in  between  feldspar  belts  and  an  octagonal  augite  grain. 


Van  Hise  might  however  suggest  that  the  present  distri- 
bution of  waters  is  a recent  phenomenon,  the  present  circulation 
being  indeed  downward,  but  much  later  than  the  origin  of  the 
copper. 

Now  if  vapors  escape  they  must  be  present  in  proportion  to 
their  vapor  pressure  in  the  lava  and  can  hardly  wholly  escape 
but  must  be  present  more  or  less  in  the  rock  moisture  of  the 
acid  interstices  which  I have  so  fully  described  for  the  in- 
trusive rocks.  But  even  in  an  effusive  as  the  rock  (above  fig- 
ure) we  see  that  between  the  crystal  of  augite  and  that  of  feld- 
spar, each  having  its  own  shape,  is  an  angular  space  which 
must  have  been  originally  a pore  filled  only  with  gas  probably. 


The  Theory  of  Copper  Deposition — Lane.  305 

In  a thoroughly  crystalized  trap,  doleritic  melaphyre  or  diabase 
the  porosity  is  not  over  1 per  cent.  But  in  the  case  of  an  amyg- 
daloid the  amount  of  vesticular  space  may  have  been  very 
considerable,  and  this  space  must  have  been  filled  either  with 
the  original  gases  or  possibly  in  the  case  pf  submarine  flows 
with  sea  water  more  or  less  contaminated  with  such  gases. 
Such  an  origin  would  readily  account  for  the  saline  character 
of  the  waters,  and  it  is  worth  noting  that  such  saline  waters 
attack  copper  as  is  shown  by  the  fixtures  around  the  salt 
baths  of  Lower  Michigan. 

Another  most  weighty  argument  is  the  occurrence  of  cop- 
per native  in  the  iron  oiks  near  Crystal  Falls.*  One  can  hardly 
imagine  this  other  than  produced  by  descending  waters  since 
the  iron  ore  is  universally  allowed  to  have  been  formed  by 
descending  waters.  Moreover  it  occurs  in  the  upper  parts  of 
iron  ore  bodies  and  is  not  known  to  have  any  connection  with 
lower  deposits.  It  may  easily  be  conceived  to  have  been  de- 
rived from  an  over-lying  extension  of  the  Keeweenawan,  now 
eroded  away. 

■ Pumpelly  supposed ' that  the  copper  may  have  been  orig- 
inally deposited  with  the  strata*  as  sulphurets  under  submarine 
conditions.  He  was  slightly  inclined  to  call  the  old  lavas  altered 
(metamorphic)  sediments. 

Irving  apparently  agreed  with  Pumpelly  speaking  of  the 
copper  having  been  arrested  in  its  descent.  The  more  recent 
writers  on  ore  deposits  however  seem  inclined  to  refer  the 
origin  of  the  copper  deposits  to  the  upward  rising  waters.  For 
instance  Posepny  writes  as  follows : 

“Some  of  the  attempted  explanations  assume,  in  my  opin- 
ion correctly,  as  the  cause  of  the  first  ore  depositions,  the  action 
of  hot  springs— in  vhPn  cont-eedon  b B only  to*  be  emphasized 
these  thermal  effects  occurred  long  after  the  intrusion  of  the 
eruptive  flows  between  the  sedimentary  strata,  so  the  ores  were 
brought,  not  by  or  in  the  eruptives  themselves,  but  by  the  later 
springs,  from  great  depths  and  perhaps  from  considerable  dis- 
tances. This  explanation,  applicable  to>  all  deposits,  suits  also 
the  exceptional  case  cited  by  R.  D.  Irving,  namely,  the  None- 

* A.  E.  Seaman  writes  that  he  has  native  copper  in  iron  ores  from  the  Cliffs 
mine  at  Iron  Mountain,  also  with  ferruginous  chert  from  the  tenth  level  of  the 
Great  Western  mine.  Crystal  Falls,  also  lrom  the  Montana  mine,  Tower, 
Minn.,  where  it  occurs  in  the  iron  ore. 


3°6 


The  American  Geologist. 


November,  1904. 


such  copper  bed  in  the  sandstone  of  Porcupine  mountain,  far 
from  an  eruptive  outflow.”  Posepny  seems  to  have  been  influ- 
enced in  the  first  place  by  a strong  prepossession  as  to  the  role 
of  ascending  solutions,  and  in  the  second  place  by  the  oc- 
currence of  the  ore  as  a mineral  or  rarely  sulfide  and  not  as 
carbonate. 

Prof.  Van  Hise  in  his  very  interesting  article  on  “Some 
Principles  Controlling  the  Deposition  of  Ores,”  uses  the  metal- 
lic copper  deposits  as  a conspicuous  illustration  of  ore  deposits 
where  the  concentration  by  ascending  waters  has  been  suffi- 
cient without  secondary  concentration  by  descending  waters, 
writing  as  follows : 

“In  some  cases  the  deposits  thus  produced  are  sufficiently 
rich,  SO'  that  they  are  of  economic  importance.  In  these  cases, 
which  undoubtedly  exist,  but  which  perhaps  are  less  numer- 
ous than  one  might  at  first  think,  a concentration  of  ascending 
waters  has  been  sufficient. 

“A  conspicuous  illustration  of  ore  deposits  of  this  class 
which  may  be  mentioned  are  the  metallic  copper  deposits  of 
the  lake  Superior  region.  The  copper  was  in  all  probability 
reduced  and  precipitated  directly  as  metallic  copper  from  up- 
ward moving  cupriferous  solutions.  The  reaucing  agents 
were  the  ferrous  compounds  in  the  solid  form,  in  part  as 
magnetite  and  as  solutions  derived  from  the  iron  bearing 
silicate*.  When  the  copper  was  precipitated,  the  iron  was 
changed  into  the  ferric  condition.  It  is  well  known  that  me- 
tallic copper  once  formed  is  but  slowly  affected  by  the  oxidizing 
action.  Oxidation  has,  in  fact,  occurred  in  the  lake  Superior 
region,  but  from  the  facts  now  to  be  observed,  not  to  an  im- 
portant extent.  An  oxidized  belt  may  have  formed  in  pre- 
Glacial  times,  but  if  so,  it  was  swept  away  by  glacial  erosion, 
and  sufficient  time  has  not  yet  elapsed  to  form  another.  The  ore 
deposits  now  worked  have  apparently  remained  practically  un- 
changed since  the  time  of  their  concentration.  In  this  fact  we 
have  the  explanation  of  the  great  richness  of  these  deposits  to 
extraordinary  depths.” 

Prof.  H.  L.  Smyth,  of  Harvard,  has  also  adopted  the 
same  belief  and  I have  already  discussed  it  in  Vol.  VI.  of  our 
reports.  Prof.  Smyth  believes  that  the  various  flows  were 
surface  weathered  and  the  earlier  non-alkaline  minerals  pro- 


The  Theory  of  Copper  Deposition — Lane.  307 

duced  thereby.  The  later  alkaline  minerals  he  believes  to  have 
been  associated  with  the  northerly  and  northwesternly  tilting, 
and  the  formation  and  the  filling  of  the  fissures  and  the  im- 
pregnation and  partial  replacement  of  amygdaloids  and  con- 
glomerates with  copper,  the  copper  not  being  derived  from 
overlying  sandstones  nor  from  traps,  but  probably  by  ascending 
solutions  from  deep-seated  sources. 

Returning  once  more  to  Prof.  Van  Hise’s  paper,  we  find 
that  however  his  theories  may  apply  to  other  deposits,  they 
apply  very  largely  to  copper-bearing  rocks.  His  first  premise 
is  that  the  greater  number  of  ore  deposits  are  the  result  of 
work  of  underground  water.  His  second  is  that  the  material 
of  ore  deposits  is  derived  from  rocks  within  the  zone  of  frac- 
ture. This  would'  seem  to  be  true,  and  shall  give  some  argu- 
ments for  believing  that  the  copper  is  derived  from  the  associ- 
ated igneous  rocks.  His  third  premise  is  that  by  far  the  major 
part  of  the  depositing  water  is  meteoric.  By  this  he  means  that 
it  is  derived  from  the  air,  rain  water  which  was  worked  down 
into  the  ground.  In  view  of  the  composition  of  the  water  at  con- 
siderable depths  above  given  on  the  Keweenawan  range,  it 
seems  probable  that  this  is  not  true,  but  that  the  largest  part 
of  the  water  may  either  have  been  buried  originally  with  the 
sediments  (possibly  he  would  class  this  as  meteoric),  or  oc- 
cluded in  the  original  magna,  as  he  suggests.  It  is  a subject 
for  further  investigation,  just  how  much  of  these  three  classes 
of  water  we  have  involved. 

His  fourth  premise  is  that  the  flowage  of  the  underground 
water  is  caused  chiefly  by  gravitative  stress.  If  this  is  true, 
and  I believe  it  is,  then  it  follows,  as  Van  Hise  himself  has 
remarked  (p.  417),  that  if  the  copper  is  most  concentrated 
along  the  higher  parts  of  the  outcrop  it  must  be  formed  by 
descending  waters;  moreover,  as  he  also  calls  attention  (p 
412)  in  case  of  the  minor  flexures  and  pitching  folds  in  the 
bed,  if  the  waters  are  descending  the  richest  parts  should  be 
in  the  troughs  of  these  folds,  or  possibly  on  lines  leading  from 
an  anticline  down  to  the  trough  of  the  folds.  Referring  once 
more  to  plate  10,  of  Vol.  VI.,  Part  II.,  it  will  be  seen  that  in 
such  a case  the  copper  of  the  Baltic  and  Trimountain  may  be 
expected  to  chute  to  the  north  when  followed  down.  So  should 
the  mines  around  Calumet,  while  the  Quincy  mine  should 


3°8 


The  American  Geologist. 


November,  1904. 


chute  southwestward.  And  yet,  as  the  flowage  of  water  is  un- 
der gravitative  stress,  it  must  be  remembered  that  it  will  take 
a considerable  difference  in  head  for  a fresh  water  to  move  or 
balance  water  with  a specific  gravity  of  (1.1898)  a fifth  more. 
However,  the  Keweenawan  series  consists  mainly  of  a great 
series  of  lava  flows,  many  of  them  over  100  feet  thick.  (See 
as  an  illustration  of  this,  the  section  of  Tamarack  shaft  No.  5, 
and  correlated  beds  elsewhere  given.)  They  are  not  likely  to 
have  lost  heat  for  a long  time  after  their  effusion,  in  fact  very 
likely  not  before  their  burial  under  succeeding  flows*  so  that 
for  thousands  of  years  the  remnant  heat  of  the  effusions  and 
the  heat  of  the  later  intrusions  may  have  aided  the  circulation, 
and  particularly  the  solvent  action  of  the  water,  as  Van  Hise 
(pp.  300,  346,  J774),  but  more  particularly  J.  F.  Kemp  and 
others  have  insisted.  And  yet  the  accumulation  of  copper  in 
the  Nonesuch  belt  of  sandy  shales,  made  up  of  lava  and  sand, 
would  indicate  that  it  is  the  chemical  character  of  the  lavas 
rather  than  their  heat  which  is  of  most  importance.  The 
source  of  the  copper  Pumpelly  considers  to  'be  sulphides  orig- 
inally deposited  and  bleached  out  and  reduced  by  the  ferrous 
iron.  This  may  be  so,  and  yet  it  is  strange  that  we  see  so 
little  of  sulphides  in  the  original  rock  or  of  sulphates  in  the 
secondary  minerals.  I have  seen  some  fine  selenite  from  the 


* In  the  succession  of  flows  noted  in  the  Isle  Royale  drill  cores  of  Vol.  VI 
and  the  Tamarack  shaft,  and  other  sections  studied  if  there  had  been  a long 
interval  between  the  flows  and  they  had  been  exposed  to  air,  the  amygdaloids 
would  have  decayed  to  red  clays  and  iron  ores,  and  if  they  had  been  long 
enough  under  water  there  would  have  been  more  or  less  deposition.  As  is 
obvious  from  the  Tamarack  section,  there  is  but  very  little  deposition,  and 
while  there  may  have  been  some  contemporary  decomposition  of  the  amygd- 
aloids— in  fact  probably  has  been,  and  it  may  have  helped  in  the  copper  concen- 
tration, yet  in  very  many  cases,  it  is  clear  that  it  did  not  progress  lar  before 
the  next  flow  came.  In  fact  in  some  cases  an  effect  on  the  marginal  grain  of 
the  underlying  flow  is  indicated.  Now.  lor  illustration’s  sake,  if  (p.  245  of  the 
Isle  Royale  report,  Fouque  and  Levy’s  observations)  an  ophite  cooling  in 
about  six  days  Jias  augite  grains  0.03  square  millimeters  in  area,  then  one 
which  has  them  about  50  square  mm.  in  area,  like  the  Greenstone  120  feet  from 
the  wall,  would  take  about  (6x5t  .03)  10,000  days  before  it  had  actually  con- 
solidated, that  is,  it  would  be  between  twenty  and  thirty  years  before  the 
center  of  a sheet  240  feet  thick  had  fully  consolidated,  and  it  would  still  be  red 
hot.  But  the  increase  of  the  grain  of  the  augite.clean  to  the  center  shows  that 
it  must  have  been  during  a very  early  stage  of  cooling,  and  at  a glance  at 
Plate  IV,  of  the  same  report  shows  that  after  more  than  ten  times  that  lapse 
of  time  say,  200  to  300  years,  the  temperature  at  the  center  would  still  retain 
something  like  an  eighth  of  its  original  excess  of  temperature  over  the  country 
rock.  The  temperature  toward  the  margin  decreases,  of  course  and  the  total 
amount  of  calorics  yet  left  in  the  flow  will  be  readily  found  by  integrating 
equation  (1 1)  or  (12)  of  the  Isle  Royale  report.  Of  course  the  above  figures 
make  no  pretense  to  accuracy.  We  have  no  right  to  apply  Fouque  and  Levy’s 
observations  on  the  grain  of  a rock  of  one  composition  off  hand  to  another. 
Yet  the  order  of  figures  is  likely  to  be  the  same,  and  it  is  plain  that  if  the 
Tamarack  cross  section  has  some  fifty  flows,  and  this  section  only  represents 
a third  or  less  of  the  whole  pile  of  flows  thus  rapidly  piled  on  each  other  there 
may  have  been  temperatures  near  boiling  ten  thousands  of  years  after  the 
formation  of  the  pile,  during  all  of  which  time  the  zeolites  we  now  see  may 
have  been  forming.  Obviously,  too,  there  will  be  a large  amount  of  energy  to 
promote  aqueous  circulation. 


The  Theory  of  Copper  Deposition — Lane.  3°9 

National  mine,  but  in  general  sulphates  are  rare.  The  arsen- 
ides and  sulphides  that  do  occur  are  very  peculiar,  occurring 
mainly  in  the  veins,  and  perhaps  rather  more  frequently  as  at 
mount  Bohemia,  associated  with  the  acid  rocks.  There  are 
signs  that  at  least  at  times  they  are  secondary  after  the  native 
copper.  It  has  occurred  to  me  that  possibly  a ferrous  or  ferric 
chloride  containing  a trace  of  copper  was  an  early  volcanic 
emanantion.  It  is,  however,  also  true  that  olivine,  which  is 
one  of  the  earliest  minerals  to  develop,  contains  ferrous  silicate 
with  which  is  likely  to  be  associated  a trace  of  copper  and 
nickel.  Furthermore,  under  the  microscope  the  olivine,  an  early 
formed  mineral,  appears  to  gather  at  the  sides  of  this  dike 
and  the  top  of  the  flow.  Analyses  (Vol.  VI.  and  here)  seem 
to  indicate  the  same  thing  in  the  variation  of  the  magnesia 
and  iron. 

Thus  the  copper  may  have  been  concentrated.  First,  with 
the  olivine  of  the  amygdaloid  traps ; secondly,  by  leaching  out 
of  the  olivine  which  decomposed  either  by  atmospheric  action 
and  meteoric  waters,  or  immediately  after  the  outflow  of  the 
lava  in  the  presence  of  the  waters,  acid  and  perhaps  hot,  buried 
with  this  formation ; thirdly,  by  reactions  due  to  the  circulation 
downward  of  this  water  set  up  by  this  uplifting  of  the  edge 
of  the  great  lake  Superior  synclinal.  It  must  also  be  remem- 
bered that  according  to  the  earlier  geologists  there  has  been 
enormous  erosion,  which,  according  to  L.  L.  Hubbard’s  theory 
(VI.,  p.  94),  may  be  in  part  replaced  by  a sliding  or  the  upper 
beds  on  the  lower  for  miles.  In  either  case  there  may  have 
been  a considerable  migration  downward,  in  the  porous  belts 
of  the  formation,  of  the  material  of  the  strata  and  the  original 
water  thereof. 

There  is  yet  much  to  be  learned,  but  three  things  appear  to 
me  to  be  extremely  probable ; the  copper  was  associated  with 
the  original  lava  flows;  that  originally  deposited  water  or  gas 
has  been  an  important  factor,  possibly  merely  in  bringing  cop- 
per into  solution,  and  that  the  water  circulation  which  finally 
precipitated  the  copper  was  downward. 

It  is  apparent,  however,  that  we  need  to  test  the  rival  theo- 
ries. We  need  to  trace  some  one  horizon  some  one  conglomer- 
ate or  flow  continuously  through  and  survey  it  carefully  and 
accurately  to  determine  the  minor  flexures.  Dr.  L.  L.  Hub- 
bard has  done  this  in  part,  but  the  work  is  not  complete. 


